Optical system having a precision angular displacement mechanism including a flat metal spring

ABSTRACT

In the precision angular displacement mechanism of an optical record and playback apparatus, the elasticity coefficient of the supporting component is kept from fluctuating caused by changes in temperature and the fatigue strength is increased. This is accomplished by making the support component of the moving section a flat metal spring. The support component of the moving section is attached with a reflecting mirror. In addition, by forming the moving section so that the position of its gravity center is located near the center of the flat metal spring, it is possible to prevent secondary resonance and torque resonance. Finally, an assembly method is disclosed that makes such a precision angular displacement mechanism easy to assemble.

BACKGROUND OF THE INVENTION

This invention relates to a precision angular displacement mechanismthat carries out tracking for an optical record and playback apparatususing a separate optical system and the method of assembling thatmechanism.

As shown in FIG. 22, in order to increase the access speed of theoptical record and playback apparatus of the prior art, it is common todivide the optical system into a shifting optical system 2 that moves inthe radial direction of an optical disk 1 and a stationary opticalsystem (not illustrated) that has a light source. Here, shifting opticalsystem 2 is composed of an object lens 3 and a mirror 4. The stationaryoptical system is composed of a light source and an angular displacementmechanism called a galvanomirror which does not move in relation tooptical disk 1.

The galvanomirror has a reflecting mirror 6 which reflects a laser light5 emitted from the light source in a direction A to a direction B andminutely displaces reflecting mirror 6 around a direction E. Thegalvanomirror also has a mechanism that tilts laser light 5 a minuteangle (θ°) in direction B. As a result, laser light 5 is reflected indirection B at reflecting mirror 6. Laser light 5 is then reflected in adirection D at a mirror 4 of shifting optical system 2 and is guided toobject lens 3. In addition, reflecting mirror 6 is minutely displaced indirection E. By tilting laser light 5 at a minute angle in direction B,a light spot 8 is always placed on a track 7 on optical disk 1 fortracking purposes.

An example of the galvanomirror of the prior art appears in FIGS. 23through 26. As shown in these drawings, coils 10a and 10b, which haveelliptical windings, are each attached to one side of a holder 9 havinga concave cross section shape. A triangular column-shaped reflectingmirror 6 is attached to the cut-out portion of the tapered part ofholder 9 by an adhesive. The tip of a holder support component 11, whichis made of resin or synthetic rubber and supports holder 9, is an insertmolded on the inner side of holder 9. The base end of holder supportcomponent 11 is attached to a support unit 12. In the middle of holdersupport component 11 is a thin hinge 11a that can change its shapeelastically.

On the two sides of holder 9 is a magnetic circuit which is composed ofmagnets 13a and 13b and yokes 14a and 14b. There is an air gap betweenthe magnetic circuit and coils 10a and 10b. Magnets 13a and 13b runalong the longitudinal direction of coils 10a and 10b. As shown in FIG.26, the direction of all magnification is in the same direction. As aresult, the magnetic field generated by magnets 13a and 13b interlinkswith coils 10a and 10b. In FIG. 26, the direction of that magnetic fieldis to the right. Because coils 10a and 10b are connected, the currentflows in the opposite direction. When current flows through coils 10aand 10b, it follows the Fleming left hand rule. As shown in FIG. 26, amagnetic force is generated in each of coils 10a and 10b. The magneticforces are in the opposite directions to each other.

As a result, when current flows through coils 10a and 10b, the magneticforce that acts in the opposite direction in coils 10a and 10b functionsas the moment that moves the moving section, which is composed ofreflecting mirror 6, holder 9 and coils 10a and 10b, around thin hinge11a. By adjusting the direction and magnitude of the moment, it ispossible to make minute adjustments to reflecting mirror 6 to adjust thedirection in which the laser light will be reflected relative toshifting optical system 2.

However, in the galvanomirror described above, because thin hinge 11a ofholder support component 11 is made of resin or synthetic rubber, therate of elasticity changes with temperature. As a result, the resonantfrequency fluctuates, reducing the control characteristics of reflectingmirror 6. In particular, when coils 10a and 10b are heated up due tocontinuous current flow, heat is conducted to holder support component11, the elasticity coefficient of thin hinge 11a decreases and theresonant frequency fluctuates.

In the galvanomirror described above, because the moving section can berotated by changing elasticity of thin hinge 11a, repetitive stress actson thin hinge 11a. In particular, at low temperatures, fatigue breakdownoccurs. Further, thin hinge 11a, which is made of resin or syntheticrubber, is commonly manufactured by means of injection molding.Therefore, there are variations in the elasticity coefficient of thethin hinge section due to variations in its dimensions caused byvariations in the molding conditions and the wear to the mold causedover time, etc. As a result, strict manufacturing control is required.

Moreover, in the galvanomirror described above, under a condition inwhich no current flows through coils 10a and 10b, the moving section,which includes reflecting mirror 6, should be at its center position. Infact, however, an offset is generated and the moving section tiltstoward one side or the other. As a result, the relative positions ofcoils 10a and 10b and magnets 13a and 13b are also offset. This resultsin reflecting mirror 6 not being able to achieve its designated angulardisplacement when the current is flowing through the coils 10a and 10b.Light spot 8 on track 7 of optical disk 1 gets into an offset conditionin which it is not accurately positioned on track 7. The cause of thegalvanomirror offset is due to the moving section being freely supportedby support component 11 of the holder or by the creeping of thin hinge11a. However, the greatest cause is due to a major fluctuation in theelasticity coefficient of thin hinge 11a due to its temperaturecharacteristics.

Furthermore, as shown in FIG. 26, in the galvanomirror described above,the magnetic field generated by the magnetic circuitry, which iscomposed of magnets 13a and 13b and yokes 14a and 14b, only interlinksto one of the two effective portions of coils 10a and 10b. This createsproblems of poor moment generation efficiency and poor balance. In otherwords, on coils 10a and 10b, which have elliptical windings, theeffective portions are the two upper and lower linear portions that runin the longitudinal direction. However, magnets 13a and 13b correspondto only one of these coils. Therefore, these magnetic fields do notinterlink to the other linear section. As a result, because theelectromagnetic force that is generated in the effective portions ofmagnets 13a and 13b and interlinks coils 10a and 10b is not symmetricalto thin hinge 11a, which is at the rotation center of the movingsection, the force not only functions as the moment centering on thinhinge 11a, but also acts as a force that causes translational motion.

This invention solves the above problems. By forming the holder supportcomponent of a flat metal spring, and by using the elastic deformationof the the flat metal spring to support the holder, to which thereflecting mirror is attached, the fluctuations in the elasticitycoefficient of the holder support component caused by the ambienttemperature can be controlled. Further, holder support component with ahigh fatigue strength can be offered. At the same time, the objective ofthis invention is to offer a method of assembling the holder and theflat metal spring by combining the synthetic resin with the flat metalspring as a single unit using insert molding.

Other objectives of this invention are to increase the generationefficiency of the magnetic force that is generated in the coils, toimprove the balance of the force that moves the moving section, toreduce the force that contributes to the translational motion of themoving section, and to offer an optical record and playback apparatusthat improves the performance of rotational motion.

SUMMARY OF THE INVENTION

The the precision angular displacement mechanism of the optical recordand playback apparatus of this invention that accomplishes the aboveobjectives comprises a shifting optical system that moves in the radialdirection of an optical disk, and a seperate stationary optical systemwhere the light source is located. The precision angular displacementmechanism reflects the laser light emitted from the light source by areflecting mirror. A light spot is formed on the track of the opticaldisk by angularly displacing of the reflecting mirror. The reflectingmirror is located in a moving section supported at the tip end of a flatmetal spring. The base end of the flat metal spring is attached toattaching means. Actuator means minutely tilts the moving section.

Here, it is desirable to have the location of the gravity center of themoving section nearly match the location of the center of the metalspring, which can change shape elastically. In addition, it is alsodesirable for the drive center line of the actuator means to be parallelto the principal axis of inertia of the moving section. Further, if thesection of the flat metal spring that changes shape elastically isnearly square in shape, the alignment of the position of the gravitycenter and the position of the drive center will be simple.

The moving section has a holder that holds the reflecting mirror. Afterinserting the resin projection formed as a single unit on the tip end ofthe flat metal spring, it is welded or cut. To insert further, theprojection may be pulled up to assemble it. The tip end of the flatmetal spring also may be an insert molded to the holder.

Finally, the flat metal spring may be an insert molded to the attachingmeans, or it may be attached to the attaching means by welding.

Here, in addition to the moving section having coils on each side of theholder, the actuator means is composed of a magnetic circuitry includingtwo magnets attached to yokes each located at an air gap from the coils.The two magnets are located symmetrically relative to the center of thecoils. It is possible to wire the two coils together in order to createa rotating moment that rotates the moving section by the magnetic forcegenerated in each coil when current flows through them.

In such a case, the yoke may have a concave section and the magnet maybe glued to the concave section. Or, instead of the two magnets, asingle magnet which has opposing polarities may be glued to the yokes.

In addition to attaching the reflecting mirror to the holder, it ispossible to provide a tilt sensor composed of a light source and areflected light volume detector at a location opposite to the reflectingmirror, attach a positioning dowel to the yoke and use the positioningdowel to position the magnet to the position of the yoke, and create astopper as a single unit on the holder.

In this invention, it is possible to minimize the fluctuations in theresonant frequency caused by fluctuations in temperature by supportingthe holder with flat metal spring. This allows an improvement in thestability when controlling the galvanomirror through servo. In addition,it is possible to improve the durability and reliability of thegalvanomirror by providing holder supporting materials with increasedfatigue strength. Stable shape dimensions can be obtained bymanufacturing the flat metal spring by means such as etching orpressing, thereby preventing the fluctuations in the elasticitycoefficient of the holder support component caused by the variations indimensions during manufacturing. Also, stable driving in a broadfrequency region can be achieved because it is possible to completelyeliminate harmful resonance caused by secondary resonance or torqueresonance, etc., since the gravity center of the moving section nearlymatches the center position of the flat metal spring and the drivecenter lines are nearly parallel to the principal axis of inertia of themoving section.

As a result, there is a remarkable improvement in the tracking controlperformance of the optical record and playback apparatus that uses theprecision angular displacement mechanism of this invention. Because ofthe single unit molding of synthetic resin to the flat metal spring, itis possible to form components that connect to the holder.Alternatively, by insert molding the flat metal spring to the holder,the connection between the holder and the flat metal spring issimplified. It is also possible to improve the assembly performance aswell as to reduce the number of parts. In addition, by using the coilseffectively in this invention, the moving section can be reduced insize, thus reducing the size of the precision angular displacementmechanism. As a result, energy savings is also achieved. This results ina sharp increase in the rotational motion performance of the movingsection to generate a well balanced electromagnetic force. Moreover, byproviding a tilt sensor, it is possible to prevent the offset thatoccurs during assembly and avoid the impact between the coils and themagnets when a stopper is provided on the holder.

Other objects and attainments together with a fuller understanding ofthe invention will become apparent and appreciated by referring to thefollowing description and claims taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an angular view of the optical record and playbackapparatus that uses the galvanomirror in the first embodiment of thisinvention.

FIG. 2A shows a side view of the galvanomirror associated with the firstembodiment of this invention.

FIG. 2B shows a cross section of the area represented by line m--m ofFIG. 2A.

FIG. 3 shows an angular view of the flat metal spring in the firstembodiment of this invention.

FIG. 4 shows a cross section of a variation of the first embodiment ofthis invention.

FIG. 5 shows an angular view of the optical record and playbackapparatus that uses the galvanomirror in the second embodiment of thisinvention.

FIG. 6 shows a side view of the galvanomirror associated with the secondembodiment of this invention.

FIG. 7 shows the cross section represented by line k--k in FIG. 6.

FIG. 8 shows the relationship between the location of the gravitycenter, the principal axis of inertia and the locations of the coils ofthe galvanomirror in the second embodiment of this invention.

FIG. 9 shows the frequency characteristics of the galvanomirror in thefirst embodiment of this invention.

FIG. 10 shows the frequency characteristics of the galvanomirror in thesecond embodiment of this invention.

FIG. 11 shows a cross section of the main components in the thirdembodiment of this invention.

FIG. 12 shows the main configuration of the galvanomirror associatedwith the fourth embodiment of this invention.

FIG. 13 shows the details of the magnetic circuitry of the fourthembodiment in FIG. 12.

FIG. 14 shows the details of the magnetic circuitry of the fifthembodiment of this invention.

FIG. 15 shows the details of the magnetic circuitry of the sixthembodiment of this invention.

FIG. 16 shows the details of the magnetic circuitry of the seventhembodiment of this invention.

FIG. 17 is an angular view of the assembly of the galvanomirrorassociated with the eighth embodiment of this invention.

FIG. 18 is a cross section of part of the galvanomirror that is viewedfrom the side, which is associated with the eighth embodiment of thisinvention in FIG. 17.

FIG. 19 is a cross section of the area represented by line A--A in FIG.18.

FIG. 20 shows an angular assembly view of the moving section of thegalvanomirror in FIG. 17.

FIG. 21 depicts the flat metal spring in FIG. 17.

FIG. 22 is an angular view that shows the general features of theoptical record and playback apparatus of the prior art.

FIG. 23 is an angular view of the major components of the precisionangular displacement mechanism of the prior art.

FIG. 24 shows a side view of the galvanomirror of the prior art.

FIG. 25 shows a cross section of the area represented by line n--n ofFIG. 24.

FIG. 26 shows the details of the magnetic circuitry of the embodiment inFIG. 23.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1-3 show the first embodiment of this invention. FIG. 1 is anoptical record and playback apparatus that is equipped with theprecision angular displacement mechanism of this embodiment. FIG. 2A isa side view of the galvanomirror associated with this embodiment. FIG.2B is a cross sectional view of line m--m in FIG. 2A. FIG. 3 is anangular view of the flat metal spring in the galvanomirror.

In the optical record and playback apparatus shown in FIG. 1, a shiftingoptical system 115 that moves in the radial direction of an optical disk119 is separated from a stationary optical system which is in a positionwhere it does not move in relation to optical disk 119. Shifting opticalsystem 115 has an object lens 118 and a mirror 116. The stationaryoptical system includes a light source 112 containing components such asa semiconductor laser, and a galvanomirror 123.

Galvanomirror 123 includes a reflecting mirror 108 which reflects alaser light 113 emitted from light source 112 to shifting optical system115 as a laser light 114. Galvanomirror 123 is equipped with a mechanismthat can tilt laser light 114 a minute angle in order to carry outprecision displacement of reflecting mirror 108 in a direction e. Asshown in FIGS. 2A and 2B, a triangular column-shaped reflecting mirror108 is attached by adhesion to a tapered cut-out portion 101a on one endof holder 101. Holder 101 is made of a light weight metal and has aconcave cross section. Coils 107a and 107b are each attached to one sideof holder 101 through an electrically insulated material.

Holder 101 is supported by a flat metal spring 102. Synthetic resinterminals 103 including projections 103a are formed as a single unit onthe tip ends of flat metal spring 102. Holder 101 has holes 101b intowhich terminals 103 are inserted. Sections 103b are formed by weldingthe portions of projections 103a that are guided outside of holes 101b.In order to prevent projections 103a from being pulled away from holes101b, holder 101 and flat metal spring 102 are bonded together.

Since a first surface 103c of terminal 103 and a second surface 101c ofholder 101 are sealed tightly, holder 101 and flat metal spring 102cannot move around relative to each other. The base end of flat metalspring 102 is tightened down by a support base 104, a locking plate 105and a screw 106 as a unit. Flat metal spring 102 is supported betweensupport base 104 and locking plate 105.

Yokes 110a and 110b are placed on one side of coils 107a and 107b,respectively. Magnets 109a and 109b are attached to yokes 110a and 110b,respectively, at an appropriate gap away from the respective coils.

FIG. 4 shows a cross section of a variation of this embodiment. In thisembodiment, flat metal spring 102 is an insert molded to a holder 111,which is made of synthetic resin. The remainder of the configuration isthe same as the embodiment shown in FIGS. 2A and 2B.

In the galvanomirror described above, the magnetic circuitry formed byyokes 110a and 110b and magnets 109a and 109b creates a magnetic field.When current flows through coils 107a and 107b, an electromagnetic forceis generated in these coils as a result of the Fleming left hand rule.This electromagnetic force functions as the moment that moves the movingsection, which is composed of holder 101, reflecting mirror 108 andcoils 107a and 107b, around point p of flat metal spring 102. As aresult of the elastic deformation of flat metal spring 102 by thismoment, holder 101 along with reflecting mirror 108 rotates around pointp as the center.

Thus, as shown in FIG. 1, laser light 113 emitted in direction x fromlight source 112 enters reflecting mirror 108, then changes its angleand is reflected as laser light 114 in direction y. Laser light 114changes its angle at mirror 116 of shifting optical system 115 and isreflected as laser light 117 in direction z. Laser light 114 is thenconverged by object lens 118 to form an optical record and playback spot121 on a track region 120 of optical disk 119. Thus the recording andplayback of information takes place.

A plurality of tracks 122 in track region 120 are for forming opticalrecord and playback spot 121. When data is recorded and played back,reflecting mirror 108 is minutely angularly displaced in direction e tominutely displace laser light 114. Thus, tracking takes place in amanner that always forms a light spot 121 on a particular track 122.

In order to access the target track in track region 120, it is common toconduct a seek operation by moving shifting optical system 115 indirection y. However, when the interval between the tracks is relativelysmall, rather than moving the shifting optical system in direction y,sometimes it shortens the seeking time to drive galvanomirror 123 andminutely angularly displace reflecting mirror 108. In addition, becauseshifting optical system 115 has a relatively large mass, there is ashort frequency band in which responses are possible. If there is a highfrequency disturbance during the positioning of the target track,tracking will no longer be possible in some cases.

In other words, when there is a desire to track in a short span of timeand the interval between the tracks is relatively small, or when thereis a desire to minimize high frequency disturbances, it is moreconvenient to carry out seeking using galvanomirror 123 described above.More specifically, by rotating reflecting mirror 108 to another angle indirection e, a laser light 124 is reflected in direction y. Laser light124 changes its angle at mirror 116 of shifting optical system 115 andis then reflected as laser light 125 in direction z. Laser light 125 isconverged by object lens 118 and a light spot 126 is formed on trackregion 120. Light spot 126 is formed on a track different from the oneon which light spot 121 is located.

By driving galvanomirror 123 in this manner to control the reflectingdirection of laser light 113 the recording and playback of informationcan be carried out by controlling the positioning of the laser light onthe target track in track region 120.

In this embodiment, flat metal spring 102 has extremely low variationsin the elasticity coefficient caused by temperature fluctuations ascompared to the resins or synthetic rubber used in the prior art. As aresult, there is no resonance frequency fluctuation and the controllingof reflecting mirror 108 is more reliable. In particular, even if coils107a and 107b are heated due to continuous current flow, the elasticitycoefficient of flat metal spring 102 will not decrease to result influctuation in the resonant frequency. Moreover, flat metal spring 102is strong in repeated bending at low temperatures, thus maintaining itsinitial characteristics over a long period of time.

Because flat metal spring 102 has only slight variations in theelasticity coefficient, the amount of offset in galvanomirror 123 isreduced to a fraction, resulting in improving the accuracy of thetracking.

As shown in FIGS. 2A and 2B, projections 103 formed on the tip ends offlat metal spring 102 may be inserted into and welded in the holes inholder 101. Alternatively, the tip ends may be inserts molded to holder101, as shown in FIG. 4.

In the embodiment described above, the magnetic circuitry is used as theactuator means to make the minute angular tilts of the moving section.However, this embodiment is not limited to the above.

The second embodiment of this invention will be described in conjunctionwith FIGS. 5-7. FIG. 5 shows an angular view of the optical record andplayback apparatus of the second embodiment. FIG. 6 shows a side view ofthe galvanomirror of this embodiment. FIG. 7 shows a cross sectionrepresented by line k--k in FIG. 6.

In the optical record and playback apparatus shown in FIG. 5, a shiftingoptical system 224, which moves in the radial direction of an opticaldisk 228, and a stationary optical system, which is in a position whereit does not move relative to optical disk 228, are separated. Shiftingoptical system 224 includes an object lens 227 and a mirror 225. Thestationary optical system is composed of a galvanomirror 232 and a lightsource 221 made from a semiconductor laser, etc.

Galvanomirror 232 includes a reflecting mirror 219 which reflects alaser light 222 emitted from light source 221 to shifting optical system224 as a laser light 223. Galvanomirror 232 also includes a mechanismthat can make precise angular displacements of reflecting mirror 219 indirection e for making precise angular tilts of laser light 223. Asshown in FIGS. 6 and 7, a triangular column reflecting mirror isattached by an adhesive to a tapered cut-out 211a on one end of a holder211. Holder 211 is made of a light metal and has a concave crosssectional shape. A balancer 220 for balancing weight is attached toholder 211 on the other side opposite to reflecting mirror 219. Inaddition, on each side of holder 211 protrudes a rib 211b. Coils 216aand 216b, which are made of flat wires, are each positioned and attachedto respective ribs 211b through electrically insulated material (notillustrated).

Holder 211 is supported by a flat metal spring 212. A synthetic resinterminal 213 and a support base 214 are formed as a single unit on thetip end and base end, respectively, of flat metal spring 212. Thesection between terminal 213 and support base 214 forms an elasticdeformation section 212a that can elastically change its shape whenholder 211 rotates. A projection 213a on terminal 213 is inserted in ahole 211b in holder 211. Thus, the relative positions of terminal 213and holder 211 are determined by inserting projecting part 213a ofterminal 213 into hole 211b of holder 211. A side surface 213b ofterminal 213 and a surface 211c of holder 211 are firmly bonded togetherusing an adhesive. The moving section, which is composed of holder 211,coils 216a and 216b, reflecting mirror 219, terminal 213 and balancer220, has its weight distributed so that the position of the gravitycenter is about at a center point q of elastic deformation section 212a.

As shown in FIG. 8, elastic deformation section 212a has a rectangularshape. The position of the gravity center of the moving section is atpoint q, which is the intersecting point of the diagonal lines onelastic deformation section 212a. For this type of gravity centeralignment, balancer 220 may be attached to holder 211 as a counterweight. Alternatively, the shape of holder 211 may be changed so that itis balanced, in which case balancer 220 need not be used. The principalaxis of inertia of the moving section nearly matches a center line t--t,which passes through center point q of elastic deformation section 212a.The gravity center alignment and the principal axis of inertia alignmentbecome easy by making the shape of elastic deformation section 212arectangular.

Yokes 218a and 218b are placed on one side of coils 216a and 216b,respectively. Magnets 217a and 217c are attached to yoke 218a at anappropriate distance from coil 216a. Similarly, magnets 217b and 217dare attached to yoke 218b at an appropriate distance from coil 216b.Coil 216a is placed in a position symmetrical to magnets 217a and 217c.Similarly, coil 216b is placed in a position symmetrical to magnets 217band 217d. Thus, according to the Fleming left hand rule, the locationsof the electromagnetic force generated in coils 216a and 216b, shown asdrive center lines r--r and s--s in FIG. 8, pass through the centerposition of each of coils 216a and 216b. In addition, drive center linesr--r and s--s are nearly parallel to center line t--t that passesthrough center point q of elastic deformation section 212a.

In galvanomirror 232 as described above, the magnet circuitry formed byyokes 218a and 218b and magnets 217a, 217b 217c and 217d creates amagnetic field. When current flows through coils 216a and 216b,electromagnetic force is generated in these coils according to theFleming left hand rule. This electromagnetic force functions as themoment that rotates the moving section around center line t--t. Sincepoint q, which is the rotation center point, matches the position of thegravity center of the moving section, the moment does not function as anextra force that attempts to cause the moving section in translationalmotion. It functions only as the moment around center line t--t. As aresult, holder 211 rotates in a stable condition around point q by theelastic deformation of elastic deformation section 212a.

FIG. 9 shows the frequency characteristics of the galvanomirrorassociated with the first embodiment. FIG. 10 shows the frequencycharacteristics of the galvanomirror of this embodiment. It is dear thatthe harmful resonance is eliminated in FIG. 10. The harmful resonance iscaused by the secondary resonance and the torque resonance of the flatmetal spring, etc. As shown in FIG. 9, a resonance peak caused by theprimary resonance of the flat metal spring occurs in the 100 Hz region.Furthermore, a resonance peak caused by the secondary resonance of theflat metal spring occurs in the 500 Hz region. In the region between theresonance peaks caused by the primary resonance and the secondaryresonance is the resonance peak caused by the torque resonance of theflat metal spring. However, as shown in FIG. 10, the secondary resonanceis minimized in this embodiment because point q, which is the rotationcenter of the moving section, is matched with the position of thegravity center of the moving section. The resonance peak caused by thetorque resonance is also minimized because drive center lines r--r ands--s of coils 216a and 216b are parallel to the principal axis ofinertia of the moving section. This embodiment has extremely goodfrequency characteristics in a broad frequency region from the lowfrequency region to the high frequency region. The frequencycharacteristics of FIGS. 9 and 10 each show the ratio of the rotationangle of the galvanomirror and the input current in the coils indecibels in the frequency region.

When controlling the galvanomirror through servo, primary resonance isnot a particular problem. However, since secondary resonance causesoscillation in servo system, it is impossible to control thegalvanomirror through servo in the frequency region where secondaryresonance occurs. It is also impossible to have the operating frequencyband within the servo control band. When a frequency of secondaryresonance is in the servo band, it is necessary to use a notch filter inorder to eliminate the resonance present. However, it is difficult tocompletely eliminate secondary resonance. Moreover, if the notch filteris used, it will make the galvanomirror drive circuitry more complex.

In this embodiment, elastic deformation section 212a is made of a flatmetal spring. However, a plurality of flat metal springs may be used ora plurality of elastic deformation sections may be formed on one flatmetal spring. In this case, the weight of the moving section should bedistributed so that it balances the respective spring constants of theelastic deformation sections with the respective elastic deformationsections. Each individual weight component that is distributed should beput on the respective elastic deformation section.

FIG. 11 shows the third embodiment of this invention. As shown in FIG.11, a reflecting mirror 337 is attached to a holder 338 by an adhesive.The holder has a concave cross section and is formed as a single unitwith a flat metal spring 340. Balancers 341 and 344 are attached to theother side of holder 338, opposite to reflecting mirror 337. On eachside of holder 338 protrudes a convex section 338a. Coils 339a and 339bare attached to respective convex sections 338a. Yokes 346a and 346b arerespectively placed on each side of holder 338. Magnets 345a, 345c andmagnets 345b, 345d are respectively attached to yokes 346a and 346d atan appropriate distance from coils 339a and 339b.

A part of flat metal spring 340 is welded by laser to a base 342, whichhas an L-shaped cross section, to form a laser welded section 343. Ahole 342a in base 342 is for attaching to and tightening down thegalvanomirror on the main unit base (not shown). Flat metal spring 340has an elastic deformation section 340a between holder 338 and base 342.In the longitudinal direction, the flat metal spring is rectangular inshape.

The moving section, which is composed of reflecting mirror 337, holder338, balancers 341 and 344 and coils 339a and 339b, is balanced inweight so that the position of the gravity center is approximately at apoint u of elastic deformation section 340a. The principal axis ofinertia of the moving section, which is vertical to the paper and passesthrough point u in FIG. 11, is nearly parallel to the drive center linesof coils 339a and 339b, which pass through points v and w vertically inFIG. 11.

In the galvanomirror as described above, the magnetic circuitry, whichis composed of yokes 346a and 346b and magnets 345a-345d, creates amagnetic field. When a current flows through coils 339, electromagneticforce is generated in the coils according to the Fleming left hand rule.This electromagnetic force functions as the moment around point u onflat metal spring 340. Holder 338 can thus rotate mainly around point uby the elastic deformation of elastic deformation section 340a. Theincoming laser light will change angle and be reflected. When thegalvanomirror is driven in the frequency region, the frequencycharacteristics will be like those shown in FIG. 10.

The fourth embodiment of this invention is shown in FIGS. 12 and 13.FIG. 12 shows the major portion of the galvanomirror associated withthis embodiment. FIG. 13 depicts an overview of the magnet circuitry. Asshown in FIG. 12, a reflecting mirror 401 is attached to a holder 402.On each side of holder 402, respective elliptical coils 403a and 403bare attached. A laser light 406a changes direction at reflecting mirror401 to become a laser light 406b. Two magnetic circuits are placed onrespective sides of the moving section with an air gap in between. Themoving section is composed of reflecting mirror 401, holder 402 andcoils 403a and 403b. In each magnetic circuit, there are two magnets404, the polarity directions of which are opposite to each other. A yoke405a is placed at one side of coil 403a. Magnets 404a and 404b areattached to yoke 405a symmetrically relative to coil 403a.

Here, a magnetic direction 408a of magnet 404a and a magnetic direction408b of magnet 404b are opposite, as indicated by the arrows. As shownin FIG. 13, the magnetic flux generated from magnet 404a creates fluxcurves that cover coil 403a while moving toward magnet 404b, forming amagnetic field. In the same manner, a yoke 405b is located at one sideof coil 403b. Magnets 404c and 404d are attached to yoke 405bsymmetrically relative to coil 403b. Here, magnetic direction 408a ofmagnet 404c and magnetic direction 408b of magnet 404d are opposite, asindicated by the arrows. The magnetic flux generated from magnet 404dcreates flux curves that cover coil 403b while moving toward magnet404c, forming a magnetic field.

As a result, when current flows through coil 403a in the direction ofarrow 407a and through coil 403b in the direction of arrow 407b,electromagnetic force is generated in coil 403a in the direction ofarrow 409a and in coil 403b in the direction of arrow 409b. This forcegenerates a torque centered on the axis parallel to the rotation centerof the moving section. The torque rotates the moving section and allowsprecision tracking to take place.

Because the magnetic circuitry of this embodiment has magnets 404a,404b, 404c and 404d, which are magnetically different relative to eachcoil, 403a and 403b, it is possible to generate electromagnetic force ofthe same strength relative to the two effective portions of each coil,403a and 403b. For this reason, the ratio of the torque to the inertiamoment of the coils is approximately twice as large as that of themagnetic circuitry in the prior art. As a result, it is possible toreduce the coil inefficiency, reduce the size of the coils, make themoving section lighter in weight, and reduce the size of the precisionangular displacement mechanism. Since the electric power supplied to thecoils can be reduced, energy saving is also achieved.

Moreover, there is a force from a component of the electromagnetic forcegenerated in the effective portion of coil 403a relative to magnet 404athat is not the torque around the axis parallel to the rotation centerof the moving section. There is also a force from a component of theelectromagnetic force generated in the effective portion of coil 403brelative to magnet 404d that is not the torque around the axis parallelto the rotation center of the moving section. Because these forces arein opposite directions and because they are of the same magnitude, theycancel out each other. In addition, because the same results can beobtained with magnets 404c and 404b, the force that contributes to thetranslational motion of the moving section decreases. Thus, in general,the force that functions in the moving section is only the torque aroundthe axis parallel to the rotation center of the moving section. This isbetter balanced than in the magnetic circuitry of the prior art andallows a sharp increase in the rotation performance of the movingsection.

If the rotation center of the moving section and the center of thetorque are matched up, the rotation motion performance of the movingsection would increase even further. As for the positions of themagnets, the same effect would be obtained if the positions of magnet404c and 404d are switched and if the positions of magnets 404a and 404bare switched. As for coils 403a and 403b, if an air core coil, whichuses no bobbin, is used, the inertia moment would become even smaller.If a coil with a wound flat magnet wire is used, the coil space factorwould increase, reducing the volume of the coil required to generate atorque of the same magnitude and at the same time reducing the inertiamoment. This would lead to a reduction in the size and an energy savingsof the precision angular displacement mechanism.

FIG. 14 shows the magnetic circuitry associated with the fifthembodiment of this invention. This embodiment is a variation of thefourth embodiment. In this embodiment, magnets 404a and 404b and magnets404c and 404d are respectively securely attached together on yokes 405aand 405b respectively. In this way, the magnetic flux that passesthrough coils 403a and 403b increases even more compared to that of thefourth embodiment, generating a torque more efficiently.

FIG. 15 shows the magnetic circuitry associated with the sixthembodiment of this invention. This embodiment is a variation of thefifth embodiment. In this embodiment, magnets 404a and 404b and magnets404c and 404d each pair are placed inside a concave portion of yokes405a and 405b and attached together without a gap. In this way, themagnetic flux that is close to the end surface areas of magnets 404a,404b, 404c and 404d at yokes 405a and 405b is more at a right anglerelative to coils 403a and 403b compared to the fourth and the fifthembodiments. This increases the torque component of the electromagneticforce generated, resulting in generating even more efficient torque.Moreover, when the surfaces of magnets 404a, 404b, 404c and 404d, andthe surfaces of yokes 405a and 405b that face the coils 403a and 403bare matched up, torque can be generated with even greater efficiency.

FIG. 16 shows the magnetic circuitry associated with the seventhembodiment of this invention. This embodiment is also a variation of thefifth embodiment. In this embodiment, the individual magnets, 404e and404f, both of which have magnetically opposing polarities, are attachedto yokes 405a and 405b, respectively. In this way, the same effects asthat in the fifth embodiment can be obtained. In addition, the number ofparts required can be reduced, increasing the assembly efficiency.

FIGS. 17-19 show the eighth embodiment of this invention. FIG. 17 showsan angular view of the assembly of the galvanomirror of this embodiment.FIG. 18 shows a cross sectional portion of the galvanomirror of thisembodiment viewed from one side. FIG. 19 shows the cross section of lineA--A in FIG. 18. As shown in these drawings, yokes 802 and 803 are eachplaced on one side of a base 801. A support base 804 is located on theupper surface of base 801. A holder 806 is supported by a flat metalspring 805 on support base 804. On one end of holder 806 is a taperedsurface to which a triangular column shaped reflecting mirror 807 isattached. On both surfaces of holder 806 are elliptical coils 808a and808b. A laser light emitted from a light source (not illustrated) issent to reflecting mirror 807, which allows the laser light to be outputto the shifting optical system (not illustrated).

Coils 808a and 808b are connected to the power supply (not shown)through a lead wire 809. On yoke 803 are two magnets 810a and 810b thatare opposite to coil 808a. On yoke 802 are two magnets 810c and 810dwhich are opposite to coil 808b. Each pair, magnets 810a and 810b andmagnets 810c and 810d, face the coils with different polarities and areadjacent to each other without gaps. Also, magnets 810a and 810b andmagnets 810c and 810d are positioned on yokes 802 and 803 using dowels811 attached to yokes 802 and 803 so that coils 808a and 808b can bepositioned accurately in a symmetrical position to each other.

By using dowels 811 in this manner to accurately position magnets 810a,810b, 810c and 810d, it is possible to adjust accurately the drivecenter lines of coils 808a and 808b to the principal axis of inertia ofthe moving section. Stoppers 816 may also be provided on holder 806 toprevent the deformation of flat metal spring 805 and to avoid impact oncoils 808a and 808b and magnets 810a, 810b 810c and 810d when a largeamount of current passes through coils 808a and 808b. A reflectingmirror 815 is attached to the bottom surface of holder 806. Also, a tiltsensor 812 is located in a position opposite to the reflecting mirror.This tilt sensor 812 is inserted from the bottom into a hole that runsfrom the top to the bottom of base 801. The sensor is pushed into placeon base 801 by a sensor spring 813.

The angular adjustment of flit sensor 812 can be achieved by using asensor adjustment screw 814 to adjust the interval between sensor spring813 and base 801. Tilt sensor 812 is composed of a light source and areflected light volume detector. The reflected light volume detectordetects the amount of light reflected at reflecting mirror 815. Thismakes it possible to detect the angle of holder 806 and reflectingmirror 815. A flexible printed circuit board 816 is connected to thetilt sensor by soldering. The amount of reflected light detected by tiltsensor 812 is input tea control circuit (not shown) and used forcontrolling the moving section. By using the tilt sensor in this manner,the offset that occurs during assembly can be prevented.

The method of assembling the moving section of the galvanomirror will bedescribed with reference to FIGS. 20 and 21. As shown in FIG. 20, aterminal 905 and a support base 906 each are formed as a single unit onthe tip end and the base end of a flat metal spring 904 respectively. Asshown in FIG. 21, the section between terminal 905 and support base 906of flat metal spring 904 is an elastic deformation section 904a. Aprojection 907 protrudes from a top surface 905c of terminal 905.Press-in sections 905b are formed on two sides of terminal 905 indirection Y. Projection 907 has a tapered shape in which the widthbecomes smaller near the tip. It has two reference surfaces 907a indirection X.

In addition, a holder 901 has a concave section into which terminal 905fits. A reflecting mirror 902, which forms a triangular column, isattached at the tapered section at one end of the holder. Balancer 903is attached to the opposite end. At the center of holder 901, a hole901a is formed for inserting projection 907 of terminal 905.

As a result, by inserting projection 907 in hole 901a, direction X isdesignated by a reference surface 907a. Furthermore, by pushing press-insections 905b of terminal 905 into the concave section of holder 901,direction Y is designated. The direction may also be designated bysimply placing press-in sections 905b in contact with the holder andapplying an adhesive. In addition, direction Z is designated by placingtop surface 905c of terminal 905 in contact with holder 901.

Here, in order to prevent the deformation of flat metal spring 904during assembly, terminal 905 may be fitted into holder 901 by raisingprojection 907 of terminal 905. After assembly, that part of projection907 that protrudes from holder 901 will be cut off. This is particularlyeffective when the holder is very rigid.

As described above, the precision angular displacement mechanism of thisinvention is extremely effective as a tracking actuator of an opticalrecord and playback apparatus with separated optical systems. It isespecially effective as a tracking actuator that demands a high level ofcontrol characteristics, assembly capability and environmentalcharacteristics. In addition, it may be used for galvanomirrorapplications involving scanning such as a laser printer.

While the invention has been described in conjunction with severalspecific embodiments, it is evident to those skilled in the art thatmany further alternatives, modifications and variations will be apparentin light of the forgoing description. Thus, the invention describedherein is intended to embrace all such alternatives, modifications,applications and variations as may fall within the spirit and scope ofthe appended claims.

What is claimed is:
 1. An optical system for use with an optical disk,comprising:stationary optical system means including:a light source forsupplying a laser beam, and angular displacement means including:amoving section comprising a reflecting mirror, responsive to the lightsource, for reflecting the laser beam, and a holder attached at its oneend to the reflecting mirror, a flat metal spring attached at its tip tothe holder for supporting the holder, a base on which the metal springis mounted, and actuator means for rotating the moving section around apredetermined point on the flat metal spring so as to minutely tilt thereflecting mirror at precision angles for placing a laser light spot ona desired track of the optical disk; and shifting optical system means,radially movable relative to the optical disk and receiving the laserbeam reflected from the reflecting mirror, for providing the reflectedlaser beam to the optical disk for carrying out record and playbackoperations.
 2. The optical system of claim 1, wherein:the moving sectionfurther includes two coils each attached on one side surface of theholder; the actuator means includes two magnetic circuits each disposedat one side of the holder, each magnetic circuit comprising a yoke andtwo magnets attached to the yoke, with the two magnets being positionedat an air gap from a respective coil and positioned symmetricallyrelative to the center of the coils; wherein the two yokes of the twomagnetic circuits are disposed parallel to each other; the two magnetsof each magnetic circuit are arranged with their polarity directionsbeing opposite to each other so as to increase the magnetic flux in apredetermined direction to increase an electromagnetic force generatedby the coils when current flows through the coils; and wherein whencurrent flows through the coils, an electromagnetic force is generatedin the coils to cause the moving section to rotate.
 3. The opticalsystem of claim 2, wherein the two magnets of each magnetic circuits areattached together.
 4. The optical system of claim 2, wherein each yokehas a concave section and the two magnets are attached to the concavesection of the yoke.
 5. The optical system of claim 2, furthercomprising a plurality of positioning dowels mounted on each yoke, thedowels being arranged in a U pattern in which the respective magnet ismounted on the respective yoke.
 6. The optical system of claim 2,further comprising a plurality of stoppers attached on the holder andeach facing a respective magnet for preventing a respective coil fromcontacting the respective magnet.
 7. The optical system of claim 1,wherein:the moving section further includes two coils each attached onone side surface of the holder; the actuator means includes two magneticcircuits each disposed at one side of the holder, each magnetic circuitcomprising a yoke and a single magnet attached to the yoke, with themagnet having two opposing polarities, the magnet being positioned at anair gap from a respective coil and positioned symmetrically relative tothe center of the coils; wherein the two yokes of the two magneticcircuits are disposed parallel to each other; the magnet of eachmagnetic circuit is arranged so as to increase the magnetic flux in apredetermined direction to increase an electromagnetic force generatedby the coils when current flows through the coils; and wherein whencurrent flows through the coils, an electromagnetic force is generatedin the coils to cause the moving section to rotate.
 8. The opticalsystem of claim 1, wherein the plane which is formed by the laser beamgoing into the reflecting mirror and the laser beam coming out of thereflecting mirror is approximately the same as the plane on which themetal spring is located.
 9. The optical system of claim 1, wherein saidflat metal spring includes terminals attached at its tip for positioningand fixing said metal spring to said holder.
 10. The optical system ofclaim 1, wherein the location of the center of gravity of the movingsection nearly matches the center position of a section of the flatmetal spring that is elastically deformable.
 11. The optical system ofclaim 10, wherein a drive center line of the actuator means is nearlyparallel to a principal axis of inertia of the moving section.
 12. Theoptical system of claim 2 or claim 11, wherein the section of the flatmetal spring that is elastically deformable is nearly square in shape.13. The optical system of claim 1, wherein:the tip of the flat metalspring is insert molded to the holder.
 14. The optical system of claim1, wherein the base is made of resin and the flat metal spring is insertmolded to the base.
 15. The optical system of claim 1, wherein the flatmetal spring is attached to the base by laser welding.